Bullet Base to Ogive Variation

[Turpentine]

Guys, I got some seconds at a good price. So I added to the pile. They will work for SHTF if nothing else. I measured some samples. I have few boxes of the same in grade 1 so I measured those in comparison.
There was more variation in weight with some outliers but the majority of the seconds weighed what they were supposed to. That’s an easy enough thing to contend with.
Diameter was exactly the same. No issue there.
Base to ogive for the firsts were extremely consistent with a very small deviation. I can remember exactly but lets say 1.650 on the comparator. That’s just a for instance number.
Base to ogive on the seconds is the reason they made the seconds pile Im pretty sure. Probably 50% were exactly the same measurement as the firsts or controls so 50% 1.650. 30% were strangely exactly .005 higher so 1.655. That almost looked like what I see when I’m trying to dial a machine in. Very few were over 1.655. Maybe 5% 1.657 then 5% at 1.648. The remaining 10% were1.6525. So

Firsts 1.650
Seconds
5 @ 1.648
50 @ 1.650. Same as control or first run
10 @ 1.6525
30 @ 1.655
5 @. 1.657

So I got curious and measured samples from Lapua, Sierra, Hornady, and Nosler in a few different calibers. All first run.
Weights We’re pretty consistent.
Base to ogive for most would be within +/-.0015. One box varied +/-.0035. But in every box but 1
i found a piece or two that was off by .008 or more from the mean. Obviously an outlier in what are known to top tier premium match bullets. As a precision shooter you would want to identify and remove those I would think.
1. I doubt I’ll buy any more of the seconds but my experimental side would like to know if I shoot well enough to tell a difference If I did no sorting? For group size and velocity, and at distance. I probably will test this just a bit if for no other reason than “Because I Can”.

2. My next question would be if I did sort and only used the bullets that matched my 1st run specs by weight and bullet base to ogive would I see any change in accuracy?

3. If specs are otherwise identical, how much variation in weight does it take to see a noticeable difference at 1000 yards?
4. Even though variation exists from bullet base to ogive. When the bullet is seated in a case the cartridge base distance to the ogive for your loads would be identical. But the base depth in the cartridge will change and case capacity would vary slightly. How much does it take to make a noticeable differenceat 1000 yards?
5. If base to ogive depth varies, it should theoretically change the flight characteristics of the projectile slightly. How much of that variation would it take to make a difference at 1000 yards If velocity remained identical?
Obviously I have had way to much time on my hands. I am stuck inside with the flu. I don’t really expect answers to any of these questions but I’m sure some of you folks have experience with some of this. I’ve measured enough bullets over a long period to know even though they are from the same lot and close, they are not clones. There are some minute differences. I just wonder how much of that difference it takes to matter.

 

[wkdickinson]

Here is another factor to consider - the seating stem diameter is significantly small than the diameter of your comparitor. So when seating the bullet, your refernce point is not what the comparitor is measuring. I made a comparitor insert the size of my seat stem and have done a number of studies comparing the BTO vs. BTSS and find significant variation, at least in Berger hybrids. I doubt there is any reason to think the same would not be true for most production bullets, let alone "2nds".

 

[Rocketvapor]

That makes at least 3 length dimensions to characterize a projectile.
OAL, BTSS, BTO. Seating depth, Jump, and B.C. can be different between bullets with variations in either.

 

[6BRA]

A longer bearing surface creates more friction and more pressure..vertical.

 

[mgunderson]

Seconds can be seconds for many reasons. Some cosmetic and some dimensional. You never know for sure unless you have inside information. I might risk it for practice ammo, but not for a match. We all make that value decision differently.

 

[DaveTooley]

Years ago when I was investigating the effects of meplats on flight characteristics we were measuring actual BC's along with velocity. Here's what we found. Meplat uniformity matters. Diameter as well as shape. Ogive shape matters. Base to ogive does not matter. We tested bullets out of the same unsorted boxes that had as much as .020" difference in the base to ogive. BC's and velocities did not change. Any difference got lost in noise. Ultimate accuracy depends on many other variables. YMMV

 

[Rocketvapor]

@DaveTooley
For the same bullet OAL, a change in BTO means (to me) a change in the Ogive to tip length.
That doesn't change B.C. ?

 

[JimSC]

Think about how the seating process works. You have two fixed points. The shell holder at top of stroke and the seating stem. Neither of those points change unless you adjust the seating die or short stroke the ram. Any difference in the measurement from the base of the bullet to the ogive only affects the amount of bullet that will be inserted in the neck, or in other words the case capacity

 

[DaveTooley]

@DaveTooley
For the same bullet OAL, a change in BTO means (to me) a change in the Ogive to tip length.
That doesn't change B.C. ?

I've typed this up three times and started over. OAL can and will vary because of jacket flow in the point up die. Jacket lube, jacket ductility and to a much lesser degree the accuracy of the press stroke. BC changes with differences in the frontal area of the bullet. Obviously different ogive shapes change the BC but we don't see bullets mixed from different shaped dies but we do see variations in meplats. They have an affect on BC's. Forget OAL as that's not a valid measurement to use. I used base to ogive just looking for the wild ones.

I'll add that if your rifle is accurate then the variations in BC can't be seen on the target until you get past 600 yds.

 

[Rocketvapor]

Just for an example, I'm shooting Berger 85.5s in a 22 Nosler.
600 yds with a hope to get to 1000 after I Master 600.
I don't point, and use a Hornady seating die with their latest ELD insert.
Slight variations in BTO might make a tiny charge variation but mostly it's CBTO I try to seat to for a consistent jump. 100 bullet boxes of Bergers seem to have a small (0.005") BTO variance but the 1000 bullet box is almost all the same. I sort Short, Medium, Long and use the same for all cartridges for a single match
Thanks for your reply.

 

[DaveTooley]

Just for an example, I'm shooting Berger 85.5s in a 22 Nosler.
600 yds with a hope to get to 1000 after I Master 600.
I don't point, and use a Hornady seating die with their latest ELD insert.
Slight variations in BTO might make a tiny charge variation but mostly it's CBTO I try to seat to for a consistent jump. 100 bullet boxes of Bergers seem to have a small (0.005") BTO variance but the 1000 bullet box is almost all the same. I sort Short, Medium, Long and use the same for all cartridges for a single match
Thanks for your reply.

Whatever gives you confidence. Our mind can get way out in the weeds but most things can't be proven. The old line about theory meets reality. I never once used a chronograph to tune up my 1000 yd. rifles. In fact I never checked loads that shot well. I just shot.
I never pointed bullets. I did install tips in SMK's from 22 to 338 for the testing. We got an average BC gain of 2-3%. Trimming meplats to uniform them we lost the same 2-3%. If I was shooting past 600 yds. I would not shoot a factory bullet without trimming the meplat. I'll give up a bit of BC to eliminate the occasional wild vertical shots. Just pulling a number out of my memory. We got as much as .030+ variation in BC's on bullets out of the same box. All due to the meplat.

 

[wkdickinson]

Here is another factor to consider - the seating stem diameter is significantly small than the diameter of your comparitor. So when seating the bullet, your refernce point is not what the comparitor is measuring. I made a comparitor insert the size of my seat stem and have done a number of studies comparing the BTO vs. BTSS and find significant variation, at least in Berger hybrids. I doubt there is any reason to think the same would not be true for most production bullets, let alone "2nds".

Here is a small random sample from a box of 500 Berger 105 Hybrids, I measured last week. I know 18 is not statistically valid, but it does illustrate my point:

 

[DaveTooley]

So ba

Here is a small random sample from a box of 500 Berger 105 Hybrids, I measured last week. I know 18 is not statistically valid, but it does illustrate my point:

View attachment 1390394

So the BTSS variation was one third of the OAL variation. Kind of makes my point that OAL is not a valid number in sorting for accuracy. YMMV

 

[Straightshooter1]

So ba

So the BTSS variation was one third of the OAL variation. Kind of makes my point that OAL is not a valid number in sorting for accuracy. YMMV

Years ago when I was investigating the effects of meplats on flight characteristics we were measuring actual BC's along with velocity. Here's what we found. Meplat uniformity matters. Diameter as well as shape. Ogive shape matters. Base to ogive does not matter. We tested bullets out of the same unsorted boxes that had as much as .020" difference in the base to ogive. BC's and velocities did not change. Any difference got lost in noise. Ultimate accuracy depends on many other variables. YMMV

When I started precision reloading it took me a little while to figure all this out. It sure wasn't obvious based on what so many people posted on various websites.

I ignore BTO and pretty much jump too, except to use it to find where my lands is as a starting point. I'll sort based on BTSS in order to get consistent seating depths. Like with wkdickinson's illustration above for his Berger 105 Hybrids, after sampling my Berger 140 Hybrids often don't really need any sorting on the BTSS. But, I've found other factory bullets do need sorting. When it's common that seating bullets at .003" intervals is done to tune a load, I figure such changes in BTSS of .003" is enough to have an affect on accuracy to warrant sorting that way.

The only other bullet dimension I found that effected accuracy (for short to medium range) is when there's a significant difference in the length of the bearing surfaces. I ran a 40 round test, some time ago, where I had some .308 rounds with a .033" difference resulting in a clear effect on velocity and POI. I seldom see that kind of difference in bearing surfaces within a particular lot (surely with bulk seconds where lots seem to have been mixed). It does takes a huge difference like that to makes a difference in accuracy.

I agree, of course, that "accuracy depends on may other variables". Some variables just can't be controlled. But, I try to control all that I'm able to . . . particularly those that are shown to make a difference.

 

[geo.ulrich]

I've typed this up three times and started over. OAL can and will vary because of jacket flow in the point up die. Jacket lube, jacket ductility and to a much lesser degree the accuracy of the press stroke. BC changes with differences in the frontal area of the bullet. Obviously different ogive shapes change the BC but we don't see bullets mixed from different shaped dies but we do see variations in meplats. They have an affect on BC's. Forget OAL as that's not a valid measurement to use. I used base to ogive just looking for the wild ones.

I'll add that if your rifle is accurate then the variations in BC can't be seen on the target until you get past 600 yds.

Dave, And don't forget jackets vary in length to start with which changes the oal to start with..

 

[Ned Ludd]

Some reloaders are very concerned about bearing surface length. I don't worry about it too much for a number of reasons. For example, every time we do a seating depth test, the amount of bullet bearing surface gripped by the neck changes by whatever seating depth [length] increment is used in the test, even if the bullets used were all essentially dimensionally identical. Nonetheless, we use the results without concern that a few thousandths' difference of bearing surface in the neck completely undermined the test results. Likewise, when we seat bullets with varying bearing surface length to a uniform seating depth, the amount of bullet shank seated in the neck also changes. If one is involved in a discipline where a few thousandths difference in bearing surface/neck wall contact can make a difference that they can actually shoot, then they probably need to be concerned about it. I freely admit that I cannot shoot the difference of a merely a few thousandths' bearing surface/neck wall contact, so I don't overly concern myself with trying to length-sort bullets by BTO. If one shoots in a discipline where it does matter, have at it, but I would point out that the OP is talking about factory second bullets here. There is a limit to how far I would go with sorting factory seconds, just because.

On the other hand, I point bullets, so length-sorting bullets by OAL is one way to facilitate obtaining more uniform points. In my hands, the bullets I use (mostly Berger) seem to have pretty uniform BTO dimensions, with most of the OAL variance residing in the nose region of the bullet. For that reason, sorting these bullets by OAL is more or less analogous to sorting them by nose length. For that reason, sorting bullets by OAL can improve seating depth consistency, which I believe to be very important. As shown in the cartoon (below), there is a relationship between what I refer to as the "two critical contact points". One of these critical contact points is farther out on the ogive toward the meplat where the seating die stem contacts and pushes the bullet into the case. The other is the point at which the caliper inserts seats on the ogive just above the bearing surface. Variance in the distance between these two critical contact points will usually mean comparable variance in seating depth as measured by cartridge base-to-ogive (CBTO).

Note that both of these critical contact points lie within the nose region of the bullet. What that means is that by sorting bullets BTO will have no effect whatsoever on length variance between the two critical contact points, as they both lie outside the BTO dimension. Thus, sorting bullets by BTO will not improve seating depth consistency. Regardless, folks can sort by bullets or anything else by whatever method they believe works best for them. What I would suggest to the OP would be to sort the factory seconds by whatever the desired method is, then use each bullet sorting group individually when reloading. In other words, sort the bullets however desired, but don't ever mix them back together when reloading and/or shooting. With a sufficient number of sorted bullets, it is usually not too difficult to use a single sorted group for a single string of fire or one match, perhaps even an entire match. One can always switch to another sorting group for additional strings or matches, but I would generally try to choose an adjacent sorting group whenever possible, just to keep variance to a minimum. I would also suggest to the OP that it might be worth testing two different bullet sorting groups, preferably two groups that actually have a reasonable length variance between them (i.e. testing two extremes), side-by-side, so that it can be determined whether the length difference is one that can actually be measured on the target. If there is no major difference on the target, perhaps it is not worth the effort to length sort the bullets.

 

[mousegunner]

I bought some .224 69gr seconds from PV, I assumed and asked if they were Noslers seconds....crickets.

I've bought Nosler named seconds from another vendor and they shot sub MOA. The ones from PV were a tad over MOA. The base to ogive varied quite I bit and I sold them and bought Hornady 75gr BTHPS.

To me it seems that if you don't know the maker of bullet and don't have specific reasons for being seconds then you takes your chances. The Nosler seconds were sold as Nosler cosmetic seconds and I could shoot them in a match.

Mystery seconds will give you mystery results, maybe a 10, an 8, a 9, X ring or whatever. Good for enough for plinking and practice, not for competition, at least that's what I think.

 

[mikecr]

Just to point something out here. None of these measures hold meaning until the ogive radius is qualified.
This leads to a 2nd point; there is no measure 'to ogive'. The ogive is the entire nose.
Your measure is to a datum on the ogive, like stem or contact datums.

So then until you've qualified your datums, your numbers are meaningless.

 

[Turpentine]

Think about how the seating process works. You have two fixed points. The shell holder at top of stroke and the seating stem. Neither of those points change unless you adjust the seating die or short stroke the ram. Any difference in the measurement from the base of the bullet to the ogive only affects the amount of bullet that will be inserted in the neck, or in other words the case capacity

That was what I was making reference to in number 4

 

[Turpentine]

I've typed this up three times and started over. OAL can and will vary because of jacket flow in the point up die. Jacket lube, jacket ductility and to a much lesser degree the accuracy of the press stroke. BC changes with differences in the frontal area of the bullet. Obviously different ogive shapes change the BC but we don't see bullets mixed from different shaped dies but we do see variations in meplats. They have an affect on BC's. Forget OAL as that's not a valid measurement to use. I used base to ogive just looking for the wild ones.

I'll add that if your rifle is accurate then the variations in BC can't be seen on the target until you get past 600 yds.

Thank you sir. I appreciate your comments. I appreciate each and every one of you taking time and weighing in. There’s a lot of knowledge and experience here.